The effect of denervation and reinnervation on synaptic tranission has been widely studied. However, it is not clear thus for what the effect of such procedures is on the sub-miniature endplate potentials (sub-mepps). Mouse hemidiaphrams will be denervated by sectioning the phrenic nerve and the time course of degeneration will be followed by recording intracellularly endplate potentials (mepps). Two kinds of experiments will be conducted. First, mepps and endplate potentias will e recorded in the preparation in vitro for 12-15 hours after sectioning the nerve. The aim is to determine if mepps (classical) and sub-mepps are differentially affected by denervation. Preliminary experiments indicate that sub-mepps remain after the classical mepps have disappeared. The second kind of experiments involve sectioning the nerve and recording mepps in the reinnervating preparation (3 to 14 days after denervation). We propose that during early stages of reinnervation spontaneous activity corresponds to sub-mepps. It is also of interest to determine if the early transmitting stages endplate potentials the size of sub-mepps can be evoked. The effect of temperature on spontaneous activity will be also be studied. The percentage of sub-mepps in frequency amplitude histograms will be determined at different temperture (20-38 degree centegrate range). Preparations used in all the above proposed experiments will be examined by electron microscopy in order to find a possible morphological correlate for the sub-mepps, if any.